This invention relates to a hydraulic slack-adjusting arrangement for use in conjunction with spring-applied, hydraulic-released disk brake actuators for use on railway vehicles. Such a hydraulic slack-adjusting arrangement must ensure that a positive and precisely-controlled clearance exists between the brake shoe and the disk when the brake is released following a brake application. A positive clearance is necessary to prevent the brake shoe from creating a drag on the disk during release, a condition which can occur with use of a zero clearance-type slack adjuster. Such drag characteristics inherently require higher expenditures of locomotive power which, due to today's high cost of fuel, puts the zero clearance slack adjuster at a critical disadvantage. In turning to the positive clearance slack adjusters, however, the use of the relative contact positions between the brake shoe and the disk to set a slack-adjusting limit, is not available as it is with a zero clearance-type slack adjuster. As a consequence, to return to the positive clearance as existed before a brake application, slack adjusters to date have typically employed complicated mechanical arrangements such as a ratchet-pawl arrangement, a worm gear-worm shaft or a spindle-screw type arrangement. Each of the above-mentioned arrangements has the disadvantage of being adjustable only to the larger increments dictated by the interrelationship of the mechanical components. In addition, this interrelationship between the mechanical components, as for example, a nut threadedly engaged to a spindle element, will result in some wear of the respective components and has also been known to result in binding between the components.
Still other positive clearance slack adjusters have added hydraulic features to overcome problems associated with purely mechanical arrangements. Such arrangements have typically required complex coupling and measuring components which, by being external to the brake actuating device, have increased the overall size of the device and have resulted in higher installation and maintenance costs.